Air conveyors are commonly used for the rapid transport of large numbers of articles, such as plastic articles, between workstations. Such conveyors have a number of advantages over their mechanical counterparts, including their ability to handle containers at much higher speeds.
A typical air conveyor for conveying plastic bottles includes a pair of opposed flanges or guides, positioned apart from one another to form a defined elongated slot. The flanges are commonly covered by a top wall and laterally spaced side walls to form a channel having an inverted U-shaped configuration. A series of louvers positioned on opposing sides of the channel direct pressurized air from a plenum against the articles being conveyed.
For handling purposes, plastic preforms, bottles and containers are often formed with annular rims positioned below their neck finish. When transported by an air conveyor, the finish of the bottles or containers extend upwardly through the slot with their annular rims overlying the spaced flanges. In this manner, the bottles or containers are suspended from the flanges by their annular rims.
In the prior art, much has been done in attempts to control the force of air used to convey the articles at high speeds while at the same time avoiding high-speed impacts and undesirable accumulations, or slugs, of bottles in the system. The air pressure kept in the plenum must be high enough to overcome the friction drag force of a slug should one occur. Modulation of the blower speed is possible, but this requires motor speed control. Unfortunately, the reaction time in depleting the air stored in the plenum as well as replenishing air blown within the plenum is relatively slow in comparison to the more immediate response required in high-speed production lines.
In some cases, those in the art have attempted to position controllable dampers on either side of a fan to restrict the flow of air to a fan. By adjustment of the restriction, the speed of the articles being conveyed can be adjusted. Based upon the relatively infrequent number of spaced fans per foot of track, the control provided by such a method has its own inherent limitations.
In other prior art cases, louvers have been installed in the walls of the plenum in an effort to control the speed of single (random) bottles while applying greater force against the slugs. However, accumulated slugs can occur randomly at any place along a given conveyor span. As such, the complexity of such applications becomes neither economical nor practical.